1. Field of the Invention
This invention relates to an apparatus for optically effecting the logical operation of an image signal, and in particular to an optical logic operation apparatus suitable for executing logical operations such as NAND, NOT and NOR of a two-dimensional image.
2. Related Background Art
It has heretofore been proposed to use an apparatus in which bistable optical devices utilizing optical bistability are formed in a two-dimensional array, with a view to effecting logical operations of a two-dimensional image at a higher speed than by processing by an electronic computer.
In such a bistable optical device, a nonlinear optical output response characteristic to an optical input is obtained by a construction including a pair of Fabry-Perot resonators in the form of parallel flat plates and a medium having a nonlinear refractive effect therein.
Also, to effect logical operations between images by such a bistable optical device, it is a necessary condition to use an exciton resonance absorbing line of a semiconductor GaAs/AlGaAs of multiplex quantum wall structure having a great tertiary nonlinear optical effect or to use the effect of a variation in the refractive index of ZnS or the like by heat to provide a construction in which those media and a Fabry-Perot resonator of high finesse are combined.
However, the constructions as described above have suffered from the following problems:
(a) The high coherency of the input light with time and the fluctuation of the wavelength used must be minimized;
(b) It is difficult to make a device having a two-dimensionally homogeneous characteristic; and
(c) The construction is susceptible to disturbance (particularly temperature); and
(d) It is necessary to increase the intensity of the inputted light sufficiently because the variations of the reflective index and others of the medium in the resonator, which follow the increased intensity of the inputted light, are utilized.
On the other hand, there has been proposed in Japanese Patent Laid-Open Application 1-10225 an optical logical operation apparatus which has solved the above-mentioned problems. This apparatus is such that an PR crystal showing the photorefractive effect (PR) is arranged in a ring resonator, and an inputted image is projected onto the crystal. Regarding such PR effect, there is a description in G. C. Valley and M. B. Klein, Opt. Eng. Vol. 22, p. 704 (1983), for example.